Conductive polymers have the physical properties of general polymers as well as the electric, magnetic and optical properties of metals. Therefore, they have a wide range of applications in the fields of conventional metals and electronic materials.
Among the many interesting conductive polymers developed over the past 30 years, polyanilines, polypyrroles and polythiophenes have attracted the most attention and have been used in industrial applications and academic research.
While polyanilines are advantageous due to their low cost, they also show low heat stability and weak chemical resistance. In addition, the possible presence of benzidine moieties in the polymer backbone, which might yield carcinogenic products upon degradation, have limited their application. On the other hand, polythiophenes and polyprroles are more environmentally friendly.
In particular, poly(3,4-alkylenedioxythiophene)s in which conductivity, thermal stability and chemical resistance are enhanced by the incorporation of alkoxy-substituents at the 3,4-positions of the thiophene ring have been developed by Bayer, Germany, and used in various applications. More specially, poly(3,4-ethylenedioxythiophene) has been shown to have relatively high conductivity higher than 100 S/cm. The oxygen substituents appear to reduce the bandgap in the conducting polymer and subject it to regular condensation at the 2,5-positions during polymerization. Thus, regular polycondensation and a low band gap can provide homogeneity to give high conductivity and thermal-and chemical-stability. Poly(3,4-alkylenedioxythiophene) has a wide range of applications, as follows:
1) Antistatic agent: to prevent static generated on the surface of plastic material or polymer, such as via a coating;
2) Condenser: for use as an alternative to electrolytes;
3) Coating on PCB(printed circuit board): to minimize environmental pollution by replacing conventional metal plating;
4) Organic EL(electro-luminescence) device: for use as a hole injecting layer on an ITO(indium tin oxide) substrate.
There is also growing interest in the development of synthetic processes, new polythiophene analogues and in-place industrial applications.
This invention relates to a new method for manufacturing conducting poly(3,4-alkylenedioxythiophene)s.
In general, polythiophene is prepared from the corresponding thiophene as a monomer. The known processes for the synthesis of polythiophene involve chemical or electrochemical polymerization. The typical chemical synthesis of conductive poly(3,4-alkylenedioxythiophene) involves the oxidative polymerization of 3,4-alkylenedioxythiophene with an oxidant (Polym. Mater. Sci. Eng. 1995, 72, 319; Macromolecules, 1996, 29, 7629; Macromolecules, 1997, 30, 2582; Synth. Met. 1999, 102, 967; U.S. Pat. No. 4,987,042 (1991) and U.S. Pat. No. 4,959,430 (1990)).
For example, with 3,4-ethylenedioxythiophene and an oxidant in organic solvent, conductive poly(3,4-ethylenedioxythiophene) is obtained as a powder. When the polymerization of 3,4-ethylenedioxythiophene in the presence of oxidant is carried out in an aqueous solution using a surfactant, a colloid aqueous solution of the conductive polymer can be prepared(EP 440957, 1991; EP 553671, 1993; U.S. Pat. No. 5,792,558, 1996). The average diameter of poly(3,4-ethylenedioxythiophene) particles in the dispersions is within the range of 10 nm to 1 μm (U.S. Pat. 5,300,575, page 2).
Another chemical process for preparing poly(3,4-ethylenedioxythiophene) from 2,5-dichloro-3,4-ethylenedioxythiophene using a blended nickel catalyst, consisting of bis(1,5-cyclooctadiene)-nickel(0), Ni(cod)2 and 2,2′-bipyridyl, has also been reported (Polymer, 2001, 42, 7229; Polymer, 2002, 43, 711). This method is not desirable for practical use in industrial applications that are expected to have a low manufacturing cost. In addition, Ni-catalyzed polycondensation of poly(3,4-ethylenedioxythiophene) requires an additional reaction process to give conductive properties, a so called doping process. Polymers show conductivity in the p-doped state, while they have no conductivity in the n-doped (=dedoped) state. Polythiophenes produced by oxidative chemical polymerization are inherently conductive because the oxidant serves as a dopant.